The present invention relates to a damper using an actuator for suppressing vibration by means of an electromagnetic force. Specifically, the present invention relates to an electromagnetic suspension system suitably used for an automobile, a railway vehicle, etc.
As a conventional electromagnetic suspension system, there can be mentioned an electromagnetic suspension system disclosed in Japanese Patent Application Public Disclosure No. 2002-257189. This electromagnetic suspension system is provided between a vehicle body and an axle, and comprises an extensible member (a shock absorber) formed by a cylinder and a rod capable of displacement relative to the cylinder. A cylindrical member having a magnet (a magnetic member) attached thereto is fixed to the cylinder. A cylindrical member having a coil (a coil member) attached thereto is fixed to the rod.
In the above-mentioned electromagnetic suspension system, the following problems (1) to (3) arise, in the case of a lateral force acting on the extensible member (the shock absorber).
(1) One of the cylindrical members strongly presses the other, so that sliding resistance is generated between the magnet and the coil, respectively provided in the cylindrical members, thus preventing smooth operation of the extensible member.
(2) If a space between the magnet and the coil is radially increased to avoid the above problem (1), a gap between the magnet and the coil increases, so that a lowering of an electromagnetic force and an increase in power consumption occur.
(3) If the extensible member is imparted with an increased stiffness to solve the above problem (1), an undesirable increase in the size and the weight of the extensible member is necessary.